1. The concentration dependence of light scattering of three proteins, ovalbumin, ribonuclease A, and ovomucoid, and binary mixtures of the three proteins were measured at various compositions and pH values at total protein concentrations of up to 35 g/l, under conditions such that ribonuclease bears a net positive charge and the other proteins bear a net negative charge. The concentration dependence was interpreted in the context of three models: a statistical thermodynamic model and two extensions of the effective hard particle model generalized to allow for the presence of non-additive interactions between species in a binary mixture (D. Wu, A. Minton). 2. Experiments were performed to determine whether quantitative composition gradient light scattering experiments can be performed using a fluorescence spectrophotometer in place of a dedicated light scattering photometer. Results obtained so far are encouraging, but further work will be required in order to achieve the requisite reproducibility.